The invention relates generally to optical devices for coupling optical signals between optical components. More specifically, the invention relates to a fiber lens for coupling signals between optical components.
Various approaches are used in optical communications to couple optical signals between optical components, such as optical fibers, laser diodes, and semiconductor optical amplifiers. One approach involves the use of a fiber lens, which is a monolithic device having a lens disposed at one end of a pigtail fiber. Light can enter or exit the fiber lens through either the lens or the pigtail fiber. The fiber lens can focus light from the pigtail fiber into a spot having the required size and intensity at a selected working distance. However, prior art has limitations on how small the spot size can be to achieve the required intensity distribution and limitations on the working distance achievable while controlling the spot size and intensity distribution. For some applications, it is desirable to obtain mode field diameters as small as 2.5 to 3.0 μm while maintaining Gaussian intensity distribution at working distances larger than 5 μm. Examples of such applications include coupling of optical signals from a semiconductor optical amplifier to an optical fiber, from a high-index semiconductor or dielectric waveguide to an optical fiber, etc.
From the foregoing, there is desired a fiber lens that can produce a focused spot with a small mode field diameter and the required intensity distribution for a broad range of working distances.